1. Field of the Invention
The present invention relates to a capacitive vacuum sensor, and more particularly to an anticorrosive capacitive vacuum sensor. The anticorrosive vacuum sensor includes a diaphragm electrode section, which has high resistance to the corrosive action of any gas that would affect the performance of the diaphragm electrode when it is exposed to such gas, and can measure the degree of vacuum under such gaseous environment with high reliability and stability over a long-term lifetime.
2. Prior Art
The manufacture of electronics components or semiconductor devices or products involves a thin film deposition or etching process that must be carried out within strictly controlled vacuum equipment. This process usually proceeds within vacuum equipment that is kept at a constant pressure. The pressures that exist within the vacuum equipment are often measured by means of capacitive vacuum sensors that provide accurate pressure measuring capabilities regardless of the type of gases use.
Most of the existing capacitive vacuum sensors that are commercially available are manufactured by a mechanical machining technique. However, a micromachining technique may be used to produce more compact sensors on a massive production basis and at reduced costs.
FIG. 3 shows one typical example of a conventional capacitive vacuum sensor that may be manufactured by using the micromachining technique. This capacitive vacuum sensor includes a non-conducting substrate 2 made of glass (referred to as glass substrate) and a silicon substrate 3 that are bonded together. The glass substrate 2 has electrically conductive leads 1 that extend through the substrate 2 for providing respective electrical paths between the top and bottom sides thereof, and the silicon substrate 3 has a recess formed on either side thereof.
There is a reference pressure space 4 that is internally delimited by the silicon substrate 3 and glass substrate 2, and which is kept at high vacuum. A getter 5 is provided within the recess on the silicon substrate 3, and communicates with the reference pressure space 4 so that it can absorb any part of the gas that remains within the reference pressure space 4. In this way, the reference pressure space 4 may be kept at high vacuum.
The silicon substrate 3 includes a boron diffused silicon layer 7 that is formed on the upper surface by diffusing boron to a depth of 2 μm to 8 μm. On the bottom side, the silicon substrate 3 is partially etched, thereby exposing the above boron diffused silicon layer 7 from the bottom side. This exposed boron diffused silicon layer 7 acts as a diaphragm electrode 6. That is, the diaphragm electrode 6 is formed from silicon that contains boron diffused throughout the depth of 2 μm to 8 μm.
The diaphragm electrode 6 may deflect when a certain gas pressure from any external source is applied upon the diaphragm electrode 6. This deflection may occur in accordance with the applied gas pressure, which causes a corresponding change in the capacitance between the rigid fixed electrode 8 and diaphragm electrode 6. The change in the capacitance may be provided in the form of a corresponding electrical signal. The electrical signal is transmitted from the fixed electrodes 8 through the electrically conductive leads 1 to electrode pads 9, respectively. The electrode pads 9 are coupled to the signal processing circuit (not shown), where the signal may be processed to determine the current pressure of the gas applied from the external source.
FIG. 5(a) through FIG. 5(e) depict the process of manufacturing the conventional capacitive vacuum sensor in FIG. 3 by the micromachining technique.
Specifically, the process is described by referring to FIG. 5(a) to FIG. 5(e). In the step of FIG. 5(a), a thermally oxidized layer 10 is first formed on the surface of the silicon substrate 3 having a recess on the upper side thereof, and the portion of the thermally oxidized layer 10 located on the upper side of silicon substrate 3 is then patterned by masking.
In the step of FIG. 5(b), boron is doped into the silicon substrate 3 on its upper side so that it can diffuse throughout the thickness of 2 μm to 8 μm. The result is the boron-diffused layer 7.
In the step of FIG. 5(c), the thermally oxidized layer 10 on the upper side of the silicon substrate 3 is removed, and the thermally oxidized layer 10 on the lower side of the silicon substrate 3 is then patterned by masking.
In the step of FIG. 5(d), a getter 5 is inserted between the silicon substrate 3 obtained through the steps FIG. 5(a) through FIG. 5(c), and the glass substrate 2 that carries the electrode pads 9 on one side (upper side, in this case) and the fixed electrodes 8 on the other side (lower side) that are interconnected with each other by the electrically conducting leads 1, respectively, and the silicon substrate 3 and glass substrate 2 are anodically bonded together into a single unit substrate under a vacuum atmosphere. The single unit substrate thus obtained includes a reference pressure space 4 that is internally delimited by the silicon substrate 3 and glass substrate 2.
In the step of FIG. 5(e), when the single unit substrate including the glass substrate 2 and silicon substrate 3 bonded together is immersed in an etching liquid, such as ethylenediaminepyrocatechol (EDP) water, the glass substrate 2 and the thermally oxidized layer 10 thereon will not be etched, while the exposed area of the silicon substrate 3 that is not covered with the thermally oxidized layer 10 will be removed by etching. This etching progresses deep into the silicon substrate 10 until the boron diffused silicon layer 7 is exposed. As the ethylenediaminepyrocatechol water has no etching effect on the boron-doped silicon, the etching will stop where and when the boron diffused silicon layer 7 has been exposed. Finally, the capacitive vacuum sensor is thus obtained, and includes a diaphragm electrode 6 formed by the boron diffused silicon layer 7 that is 2 μm to 8 μm thick.
Various types of gases may be utilized during the process of manufacturing semiconductor devices or electronics components. Some of the gases may contain reactive gases that have corrosive action. When the diaphragm electrode is exposed to the reactive gases, it may be affected by the corrosive action. If the capacitive vacuum sensor includes a diaphragm electrode that is easy to be affected by the corrosive action, it may have a shorter lifetime. Thus, the capacitive vacuum sensor cannot provide the long-term reliable pressure measuring capabilities.
Particularly, in the dry etching equipment, some gases that contain fluorine reactive gases may be used in manufacturing silicon-based semiconductor devices. In this case, the capacitive vacuum sensor including the silicon-based diaphragm electrode may be used to measure the pressures in the fluorine gas atmosphere. During the process, the diaphragm electrode is always exposed to the fluorine reactive gases that have the etching effect on the diaphragm electrode. Thus, the diaphragm electrode may be damaged seriously.